1. Field of the Invention
The present invention relates to an electrically operated fuel pump apparatus for use, for example, in an automobile to pump fuel from a fuel tank to an automotive internal combustion engine. More particularly, the invention is concerned with a fuel pump apparatus of the type that comprises a regenerative pump including a pump housing and an impeller driven by an electric motor.
2. Description of the Prior Art
In the prior art pump apparatus of the class specified above, the impeller is fixed by a fixing means, such as a key, to an extension of a shaft of the electric motor. In addition, the pump housing is coaxially fitted to a motor housing or to a bearing holder of the motor with a high accuracy.
Due to this construction of the prior art pump apparatus, the precision of the axial or side clearances and radial clearance between the pump impeller and housing depends on the perpendicularity and concentricity of the pump impeller and housing relative to the motor shaft. The perpendicularity and concentricity depend on the degree of precision of the structure of the connection between the pump and motor sections of the pump apparatus, namely, partly on the degree of precision of the connection between the pump housing and either the motor housing or the motor bearing holder and partly on the perpendicularity of either the motor housing or the motor bearing holder relative to the motor shaft. Accordingly, if the end portions of the pump housing and of either the motor housing or the motor bearing holder which are to be connected together are worked with a low degree of precision, the side and radial clearances between the pump impeller and housing cannot be kept within proper dimensions and thus the pump apparatus is inoperative to provide a high pumping performance. Due to the above-discussed structure of the pump apparatus, moreover, it is difficult to form motor shaft bearings by flexible bearing mechanisms such as self-aligning bearings. This makes it difficult to easily assemble component parts of the motor.